The invention discloses an ultraviolet curing reaction-based fluoride-free and water-repellent finishing method of cotton fabric. The method comprises the steps of putting the cotton fabric into 3-mercaptopropyl triethoxysilane ethyl acetate solution and carrying out mercapto modification to obtain pretreated cotton fabric; dipping the cotton fabric subjected to mercapto modification into vinyl polyhedral oligomeric silsesquioxane solution, and obtaining the fluoride-free and water-repellent cotton fabric, which has a surface with an approximate super-hydrophobic effect, under the ultraviolet curing condition. The reaction is based on the principle of click chemistry, so that a static contact angle is basically remained unchanged after soaping treatment is carried out. Furthermore, according to a test method of AATCC 22-2005 waterproof spray test, the waterproof spray test score of the cotton fabric subjected to water-repellent finishing reaches 95. The ultraviolet curing reaction-based fluoride-free and water-repellent finishing method of the cotton fabric is simple in operation and high in efficiency, obvious in water-repellent effect under the condition that a finishing agent is fluoride-free, and high in finishing washing fastness.